1. Field of the Invention
The present invention relates to an intermediate transfer chamber, a substrate processing system, and an exhaust method for the intermediate transfer chamber. In particular, the present invention relates to an intermediate transfer chamber which is evacuated when a substrate is transferred.
2. Description of the Related Art
A substrate processing system that subjects waters as substrates to plasma processing is comprised of a process module that houses the wafers and subjects the wafers to plasma processing, a load-lock module implemented by an intermediate transfer chamber that transfers each wafer into the process module, and a loader module that removes each wafer from a container housing the wafers and transfers each wafer to the load-lock module.
In general, the load-lock module of the substrate processing system has a function of receiving a wafer under atmospheric pressure, evacuating a chamber to a predetermined pressure, opening a gate to the process module, transferring the wafer into the process module, transferring the wafer out of the process module upon completion of processing, closing the gate to the process module, returning the pressure in the chamber to atmospheric pressure, and transferring the wafer into the loader module (see e.g. Japanese Laid-Open Patent Publication (Kokai) No. 2006-128578).
Conventionally, there has been the problem that, in a process of evacuating the load-lock module, particles are produced in the chamber and become attached to and accumulate on surfaces of wafers to form defects in the wafers in wafer processing, resulting in the yield and reliability of semiconductor devices ultimately manufactured from the wafers decreasing.
As a probable mechanism for generation of particles in the chamber during evacuation, it is thought that in most cases, particles attached to and accumulated in the chamber are thrown up during evacuation and become attached to a wafer.
However, aside from the particle generation mechanism mentioned above, it has been found out that moisture in the chamber coagulates due to abrupt temperature decrease caused by adiabatic expansion of internal gas during evacuation, and as a result, particles are produced and become attached to a wafer. If a wafer with such particles attached thereto is subjected to processing, petal-shaped corrosion marks remain on the wafer, causing formation of defects in the wafer.
It has been found through observation that the temperature of internal gas decreases by about several tens ° C. during evacuation although it is heavily dependent on the type of gas, chamber capacity, exhaust velocity, and so on. If the chamber contains moisture, the moisture condenses around small particles to grow into large particles, which further coagulate into ice depending on temperature and become attached to a wafer. Even if no core particles are present within the chamber, there may be cases where the above phenomena, i.e. the condensation and the coagulation occur when the chamber contains moisture, for example, various ions in gas serve as condensation cores or water molecules flocculate into large particles, and which will cause a serious problem.